Study Shows Snake River Smallmouth Bass Between Brownlee/Swan Falls Healthy, Interconnected Population

A recent Idaho study has offered a better understanding of the behavior of smallmouth bass in the Snake River and its tributaries.

The Snake River’s smallmouth bass population attracts a lot of anglers, and spring is often when they find the largest fish. Many anglers know the large fish are often females that are in the shallows during spawning season, and some of those bass move into the Snake River’s tributaries to spawn. Some anglers wonder whether targeting those fish limits the population.

Research by a University of Idaho graduate student, in conjunction with Idaho Fish and Game, found the river’s smallmouths are rarely harvested, even in the tributaries during the spring and summer, so there is likely very little harvest impact on smallmouth reproduction.

This was just one of the findings of the study, which focused on the stretch of the Snake River between the Brownlee and Swan Falls reservoirs and was conducted in 2017-18.

Biologists wanted to better understand the smallmouth bass population upstream of Brownlee Reservoir and in the Snake River tributaries, including the Boise, Payette, and Weiser rivers. The study provided data to help biologists and anglers understand how this smallmouth population functions and whether management adequately protects fish while providing an excellent fishing opportunity.

While bass fishing between Swan Falls and Brownlee Reservoir is good in some some sections of the river and poor in others, that does not necessarily mean the fish in these sections are isolated populations. In fact, the study found that there is actually a large, interconnected smallmouth population that spans the sections within the study area.

The bass tend to be very mobile, particularly in the spring and summer, with several fish moving more than 62 miles upriver during the study, and some more than 150 miles. That number represents some of the longest movements of smallmouth bass ever recorded.

“Basically, we found that instead of having a bunch of solitary populations we have essentially one big inter-mixing population,” said Mike Peterson, fisheries biologist for the Southwest Region.

As a whole, the study showed this smallmouth population had good size distribution, and that the fish grew rapidly and were generally healthy, but they were also fairly short lived. There are plenty of fish larger than 12 inches available for anglers, and changes in the minimum length limit would have little effect on the number of larger fish available. There is currently no biological reason to change the six-fish limit, with a 12-inch minimum length for smallmouths, said IDFG in a press release about the study.

“The current management appears to be working well within the river section we studied. We’re not proposing to change anything over the next few years,” Peterson said.

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